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1071-專題演講-1071219-白偉武(台大凝態中心)

演講活動
張貼人:李明芳公告日期:2018-09-03
 
Time12/19/2018 (Wed.) 14:20~16:20
SpeakerProf.白偉武(Woei-Wu Pai)
Center for Vondensed Matter Sciences, National Taiwan University
TitleMonolayer transition metal dichalcogenides – unexpected charge density waves and an emergent topological phase
AbstractDimensionality effect can play an important role in thin film properties. Here we show that charge density waves (CDW) can either emerge or change its ordering in the single-layer limit of transition metal dichalcogenides (TMD), with no bulk counterparts. Using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy and spectroscopy (STM/STS), a (2x2) CDW of a Tc=92 K emerges in single-layer 1T-TiTe2 and vanishes in two-layer or multi-layer films[1]. The CDW leads to an unexplained pseudogap and is not reproduced in state-of-the-art ab-initio calculations. The role of impurity on CDW will be discussed. In 1T-VSe2, we observed a dramatic change of the CDW ordering pattern from (4x4) to (Ö3xÖ7), and a significant increase of the CDW transition temperature[2]. Both cases indicate that dimensionality is a route of tuning CDW properties. In monolayers of 1T-WSe2, we confirmed the predicted topological insulator phase but found an unexpectedly large gap of ~129 mV twice larger than that of 1T-WTe2[3]. This is due to different band inversion mechanisms. Ab-initio calculations and STS also support an in-gap state near the 1T-layer boundary. Our studies can be extended to more complicated heterostructures of TMDs in which unexpected electronic states may be explored or even engineered.
[1] “Emergence of charge density waves and a pseudogap in single-layer TiTe2”, P. Chen, W. W. Pai et al., Nature communications, (2017)8:516
[2] “Unique gap structure and symmetry of the charge density wave in single-layer VSe2”, P. Chen, W. W. Pai et al., Phys. Rev. Lett., 121, 196402 (2018)
[3] “Large quantum-spin-Hall gap in single-layer 1T’ WSe2”, P. Chen, W. W. Pai et al., Nature communications, (2018) 9:2003
PlaceConference Room (Basement), General Hall, Gongquan Campuses, NTNU


 
最後修改時間:2018-12-13 PM 4:51

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單位簡介

本系的重點研究領域包括:凝態物理、光電與奈米科學、高能與粒子物理、軟凝態物理與生物物理、原分子光學物理、及物理科學教育等。本系前身為臺灣省立師範學院理化系物理組,成立於民國三十五年(1946年)本校創校之始。民國五十一年(1962年)本系獨立成系,民國六十三年(1974年)成立物理研究所碩士班,民國八十年(1991年)成立研究所博士班。長久以來,本系肩負著培育臺灣中等學校物理科師資的重任,但也不忘在物理學術研究上求新求進步。至今本系培育出的學術人才已有一位中研院院士及近百位中研院研究員及大學教授,各行各業的高科技人材更是不勝枚舉。民國八十三年師資培育法改制後,本系已升級為尖端學術研究、科技應用研發、及中學師資培育三者齊備的系所。

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